The concept of holism is a very ancient one. Aristotle in his seminal work Metaphysics first introduced the idea that the whole is greater than the sum of its parts. This idea forms the basis of many different approaches that can be considered to be holistic.
Within this philosophy there is the idea that you cannot consider only one aspect of something without reference to the whole system. For example an individual human being cannot be understood without reference to the society that they life in. In 1624 John Donne had another way of putting this: "no man is an island".
When applied to our health the concept of holism suggests that there is an idea of health that encompasses our whole being. This whole health is something that must be taken into account when working on a part of our health. This implies that for holistic healing to take place focussing only on one aspect of the disease is not sufficient. What is needed is an approach which addresses all aspects.
Modern orthodox medicine has a tendency to focus only on the body. It sees the body as a machine which ordinarily runs smoothly. When something goes wrong this machine needs to be fixed and then it will work again. However this only focuses on one aspect of a human being, that we are physical beings. It does not take into account the emotional, psychological, social or spiritual aspects of being human.
Take for example one of our modern day health issues such as type 2 diabetes. At one level this is caused bay obesity and poor diet which damage the body's glucose metabolism systems. Orthodox medicine will treat this condition with drugs that help to control blood sugars and suggest that people loose weight. However this does not take into account: the reasons that someone became obese in the first place; the emotional attachment they may have to food; the societal pressures to eat junk food; etc. A truly holistic approach to diabetes would have to include addressing these other aspects as well.
However just addressing the parts that we can identify is still not addressing the whole. To do this also needs an approach which at once focussed on healing the body, working with the mind, changing society, educating about healthy lifestyles whilst also being open to the interconnectedness of all things. Hence it can be argued that holistic health would need to be engaged in healing the planet as well.